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Chapter 1

Introduction to Planet “Earth”

• The world ocean is the most prominent feature on

Earth.

• Oceans cover 70.8% of Earth’s surface.

• The origin and development of life on Earth are

connected to the ocean.

• The oceans have a long history on Earth.

Overview

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• Oceans dominate

Earth’s surface

• Earth’s largest

habitat

• 97.2% of Earth’s

surface water

Earth’s Oceans

• Earth has one

ocean.

• Divided into four

principal oceans

and one other.

– Pacific Ocean

– Atlantic Ocean

– Indian Ocean

– Arctic Ocean

– Southern, or

Antarctic, Ocean

Earth’s Oceans

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Ocean Size and Depth

• Pacific Ocean

– World’s largest ocean

• Accounts for more than half of Earth’s ocean space

– World’s deepest ocean

– Earth’s largest geographic feature

– Named in 1520 by Ferdinand Magellan

Earth’s Oceans

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• Atlantic Ocean – Half the size of the Pacific Ocean

– Shallower than the Pacific Ocean

– Separates the Old World from the New World

• Indian Ocean – Smaller than the Atlantic Ocean

– Similar depth as the Atlantic Ocean

– Primarily in the Southern Hemisphere

Earth’s Oceans

• Arctic Ocean – Seven percent the size of the Pacific Ocean

– Shallowest world ocean

– Permanent layer of sea ice a few meters thick

• Southern Ocean or Antarctic Ocean – Circumnavigates Antarctica

– Is really the parts of the Pacific, Atlantic, and Indian Oceans that lie south of 50°S latitude

Earth’s Oceans

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• Smaller and shallower than oceans

• Salt water

• Usually enclosed by land

– Sargasso Sea defined by surrounding ocean currents

• Directly connected to the ocean

The Seven Seas

• Before the 15th century, Europeans considered

the seven seas to be the following:

– Red Sea

– Mediterranean Sea

– Persian Gulf

– Black Sea

– Adriatic Sea

– Caspian Sea

– Indian Ocean

The Seven Seas

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Ancient Seven Seas Map

• Average ocean depth is 3682 meters (12, 080 feet)

• Average continental elevation is 840 meters (2756 feet)

• Deepest ocean trench is the Mariana Trench at 11,022 meters (36,161 feet)

• Highest continental mountain is Mt. Everest at 8850 meters (29,035 feet)

Comparing Oceans to Continents

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Early Exploration of the Oceans

• Early explorers used boats to seek new fishing grounds for food.

• The ocean facilitated trade and interaction between cultures.

From here to slide #30 (Oceanography Continues) Section 1.2

of your textbook is summarized but not discussed in class –

Please read it and Review questions 1 – 3 in the Concept

Check of page 15

Pacific Navigators

• No human evolution on

Pacific islands.

• Populated by voyagers.

– Polynesia

– Melanesia

– Micronesia

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• No written records exist of Pacific human history

before the 16th century.

• Archeological evidence suggests island occupation by

people from New Guinea as early as 4000–5000 B.C.

Pacific People

• Thor Heyerdahl sailed on a balsa raft - the Kon

Tiki - to demonstrate migration of South Americans

to Pacific Ocean islands.

Pacific People

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• Phoenecians - first from Western Hemisphere to

develop navigation arts

– Navigated circa 2000 B.C.

– Explored Mediterranean Sea, Red Sea, and Indian Ocean

– First circumnavigation of Africa

– Reached the British Isles

European Navigators

• Greek Pytheas

– Sailed northward using a simple method to determine

latitude in 325 B.C.

– Navigated using the North Star

• Eratosthenes determined Earth’s circumference

fairly accurately.

European Navigators

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• Herodotus produced

inaccurate world map

around 450 B.C.

• Claudius Ptolemy

produced fairly accurate

world map around 150

A.D.

– Erroneously updated

Eratosthenes’ original

circumference estimation,

later causing Christopher

Columbus to believe he

had reached Asia

Europeans

• Arabs dominant navigators in the Mediterranean Sea

• Traded extensively with East Africa, India, and

Southeast Asia

• Learned to use Indian Ocean monsoon winds for

travel

The Middle Ages

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• Vikings explored North Atlantic Ocean

– Settled Iceland and Greenland in 9th and 10th centuries A.D.

– Leif Eriksson designated part of eastern Canada Vinland

(now Newfoundland) in 995 A.D.

– Greenland, Vinland settlements abandoned by 1450 A.D.

due to climatic cooling

The Middle Ages

• Other Viking explorers

– Erik “the Red” Thorvaldson - discovered Greenland

– Bjarni Herjólfsson - first to find Newfoundland

The Middle Ages

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Viking Routes and Colonies

• Search for new Eastern trade routes by sea

– Prince Henry the Navigator of Portugal sought trade

routes around Africa.

– Europeans explore North and South America.

• Christopher Columbus was financed by the Spanish to find

new trade routes to Asia.

The Age of Discovery in Europe 1492–1522

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• Spaniard Ferdinand Magellan circumnavigated the

globe.

– Was killed on a Pacific Island in 1521

• Juan Sebastian del Caño completed the

circumnavigation in 1522.

• Voyages paved the way for the Spanish to take gold

from the Incas and Mayas.

• Spain’s maritime dominance ended when England

defeated the Spanish Armada in 1588.

The Age of Discovery in Europe 1492–1522

Voyages of Columbus and Magellan

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• Italian Giovanni Caboto, also known as John

Cabot - landed on northeastern coast of North America.

• Vasco Nuñez de Balboa - attempted land crossing at

Isthmus of Panama.

The Age of Discovery in Europe 1492–1522

• The English wanted to retain maritime superiority.

• Captain James Cook (1728–1779) undertook three scientific voyages. – Ships HMS Endeavour, Resolution, Adventure

– Mapped many islands in Pacific

– Systematically measured ocean characteristics

– Marine chronograph (longitude)

Voyaging for Science

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Cook’s Voyages

• More high-technology tools available today – Sonar

– Robotics

– Computers

– Satellites

• NOAA - National Oceanographic and Atmospheric Administration

Oceanography Continues

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• Scientific study of all aspects of the marine environment.

What is Oceanography?

• Natural phenomena governed by physical processes

• Physical processes similar today as in the past

• Scientists discover these processes and make

predictions.

• Called the scientific method

Nature of Scientific Inquiry

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The Scientific Method

• Science never reaches absolute truth.

• Truth is probable and based on available

observations.

• New observations yield scientific progress.

• In reality, scientists have no formal method.

• Theory - well-substantiated explanation of some

aspect of the natural world.

Theories and Truth

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• Nebular hypothesis - all bodies in the solar system formed from nebula – Nebula = cloud of gases and space dust

• Mainly hydrogen and helium

Formation of Earth and the Solar System

• Gravity concentrates material at center of cloud (Sun).

• Protoplanets form from smaller concentrations of matter (eddies).

Nebular Hypothesis

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• Larger than Earth today

• Homogeneous composition

• Bombarded by meteorites – Moon formed from collision with large asteroid.

Protoearth

• Radioactive heat – Spontaneous disintegration of atoms

– Fusion reactions

• Heat from contraction (protoplanet shrinks due to gravity)

• Protoearth partially melts

• Density stratification (layered Earth)

Protoearth

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Solar System Today

• High density = heavy for its size

• Early Earth experienced gravitational separation. – High-density materials (iron and nickel) settled in core.

– Less dense materials formed concentric spheres around core.

Density Stratification

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• Layers defined by – Chemical composition

– Physical properties

Earth’s Internal Structure

• Crust – Low-density, mainly silicate minerals

• Mantle – Mainly iron (Fe) and magnesium (Mg) silicate minerals

• Core – High-density, mainly iron (Fe) and nickel (Ni)

Layers by Chemical Composition

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• Lithosphere

• Asthenosphere

• Mesosphere

• Outer core

• Inner core

Layers by Physical Properties

• Cool, rigid shell

• Includes crust and upper mantle

• About 100 km (60 miles) thick

Lithosphere

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• Relatively hot, plastic

• Flows with high viscosity – Important for movement of lithospheric plates

• Base of lithosphere to about 700 km (430 miles) deep

Asthenosphere

Internal Structure of Earth

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Continental vs. Oceanic Crust

• Vertical movement of Earth’s crust

• Buoyancy of lithosphere on asthenosphere – Less dense continental crust floats higher than denser

oceanic crust.

• Isostatic rebound - rising of crust formerly weighed down by glacier ice

Isostatic Adjustment

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Isostatic Adjustment

• Outgassing - occurred during density stratification – Water vapor

– Carbon dioxide

– Hydrogen

– Other gases

• Earth’s early atmosphere different from today

Origin of Earth’s Atmosphere

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• Outgassed water vapor fell as rain.

• The first permanent oceans formed 4 billion years ago.

• Salinity developed from dissolved rock elements. – Early acidic rain dissolved more crustal minerals than

today.

Origin of Earth’s Oceans

Development of Earth’s Oceans

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• Earth’s earliest known life forms are 3.5-billion-year-old bacteria fossilized in ocean rocks.

• These are the building blocks for life on early Earth.

• There is no direct evidence of early Earth’s environment.

Life’s Possible Ocean Origins

• Humans require O2.

• Ozone (O3) protects from ultraviolet radiation.

• Early Earth had little free oxygen.

• The lack of ozone may have helped originate life.

Oxygen

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• Organic molecules formed by ultraviolet light, electrical spark (lightning), and a mixture of water, carbon dioxide, hydrogen, methane, and ammonia

Stanley Miller’s Experiment

• Organisms adapt and change through time.

• Advantageous traits are naturally selected.

• Traits are passed to the next generation.

• Organisms adapt to environments.

• Organisms can modify environments.

Evolution and Natural Selection

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• Heterotrophs – Very earliest life

– Require external food supply

• Autotrophs – Evolved later

– Manufacture own food supply

Plants and Animals Evolve

• Probably similar to modern anaerobic bacteria – Survive without oxygen

• Chemosynthesis from chemicals at deep hydrothermal vents

• Supports idea of life’s origins on deep ocean floor in absence of light

First Autotrophs

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• Complex autotrophs developed chlorophyll.

• This allowed the use of the Sun for photosynthesis.

• Cellular respiration

Photosynthesis and Respiration

Photosynthesis and Respiration

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• 2.45 billion years ago

• Increased oxygen and ozone eliminated the anaerobe food supply.

• Light and oxygen kill anaerobes.

• Cyanobacteria adapted and thrived.

Great Oxidation Event

Plants and Earth’s Environment

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• Photosynthetic organisms are responsible for life as we know it today.

• Reduce CO2, increase O2 to 21%

• High oxygen = biodiversity increase

• Low oxygen associated with extinction events

Changes to Earth’s Atmosphere

Geologic Time Scale